1. Field of the Invention
The present invention relates to an air-filtering material adapted to be exchangeably attached to an air filter, particularly an air filter mounted in an automobile engine, and having improved cleaning efficiency or dust collectability.
2. Prior Art
Among various prior art air-filtering materials, it has been proposed to employ a nonwoven fabric of a type in which fiber staples are interlocked with each other by needle punching to form a sheet-like web. Such needle punching type nonwoven fabrics, however, inherently include a number of bits formed by penetration of needles of a needle punching machine. Since the needles of the needle punching machine have relatively large diameter and are relatively widely spaced each other, the bits once formed by penetration of the needles could not be filled up by centripetal movement of the fiber staples surrounding the bits. When the bits remain in the needle punching type nonwoven fabric its air-filtering efficiency would be greatly degraded.
Although some attempts have been made to minimize the needle bits by selecting kind and diameter of the staple fibers, no remarkable improvement could yet be found. It has also been attempted that the fiber staples are impregnated with resin to substantially stop up the needle bits. This will surely improve the dust collectability but shorten a life span of the air-filtering material due to a greater power loss.